1. Field of the Invention
The present invention relates to a hydraulic control system for controlling a flow control valve to drive a hydraulic actuator in response to operation of a control device (such as a control lever or control pedal). More particularly, the invention relates to a control system for controlling a hydraulic actuator or actuators mounted on a working vehicle such as a backhoe or loader.
2. Description of the Related Art
Hydraulic actuator control systems for working vehicles as noted above are disclosed in U.S. Pat. No. 5,046,312 and Japanese Patent Publication Kokai No. 2-256901, for example.
These systems include a swiveling hydraulic motor acting as a hydraulic actuator, an electromagnetic proportional flow control valve for receiving pressure oil from a pump to control the hydraulic motor, a control lever, and a position sensor for detecting control positions of the control lever. According to such a construction, when the control lever lies in a neutral stop position, the position sensor detects this state. Based on a detection value provided by this sensor, the flow control valve is operated to a neutral position to stop the hydraulic motor. As the control lever is operated from the neutral stop position to an operative position, a control electric current is outputted to the flow control valve to cause the flow control valve to supply pressure oil at the higher flow rate the greater the amount of operation of the control lever. Consequently, the flow control valve is switched from the neutral position to a pressure oil supplying position.
Thus, the hydraulic motor is operable at the higher rotating rate, the greater amount the control lever is operated from the neutral stop position. By selecting a control position of the control lever, the hydraulic motor may be driven at a desired speed.
An agreement between control position of the control lever and operating speed of the hydraulic motor may be maintained, provided that the control position of the control lever and the operating speed of the hydraulic motor remain constant under any load conditions and characteristics of all elements forming hydraulic circuitry.
However, where, for example, each flow control valve manufactured has a different characteristic to other flow control valves, the flow control valve in each system, e.g. each backhoe, has a different amount of operation corresponding to a certain control position of the control lever. This could result in a different flow rate of pressure oil from the flow control valve. That is, even when the control lever is operated the same amount, a hydraulic actuator such as a hydraulic motor in each system may be operated at a different rate.
Further, even if an amount of operation of the flow control valve corresponding to a control position of the control lever is the same for different working vehicles, variations in the flow rate of pressure oil from the pump to the flow control valve would result in variations in the flow rate of pressure oil from the flow control valve. Consequently, when the control lever is operated the same amount in each operating condition, the hydraulic actuator may be operated at a different rate.